It is generally known that the use of straight vacuum residue for road asphalt produces a road cover of inferior quality from the standpoint of durability because the paraffin components of the vacuum residues are readily biologically degradable. In time the asphalt cover loses its coherence and becomes brittle. The same problems could occur with liquid coal extracts which also contain heat-sensitive materials called asphaltenes but which are not chemically the same as petroleum asphaltenes. In any event, various deasphalting processes have been developed in order to obtain a more paraffin-free asphaltic product. The deasphalting process, in general, consists of extracting the heptane solubles from the asphaltenes. The "asphaltenes" are defined as materials which are insoluble in pentane or heptane at ambient temperatures, but soluble in benzene. The asphaltene materials are also considered to be "heat labile," in that they coke readily at temperatures above about 700.degree. F. Typically the solvents used in "de-asphalting" operations to separate the heptane solubles from the asphaltenes are propane and mixtures of propane, butane and pentane.
It has, however, recently been determined that the various groups of compounds making up these mixtures called "asphaltenes" still contain up to 40% to 60% of material soluble in heptane at elevated temperatures. This discovery came to light from a new analytical method designed to analyze recovered asphaltenes and reference may be made to: A.P.I. Research Project 60, Report No. 13, "Characterization of the Heavy Ends of Petroleum," July 1, 1972, to June 30, 1973. In essence, it appears that the high percentage (up to 60%) of microcrystalline waxes remains because they are soluble in heptane at its boiling point of about 100.degree. C., while only soluble to a small extent at ambient temperatures. In the standard asphaltene test, where there is testing with pentane or heptane at ambient temperatures, the microcrystalline waxes are practically insoluble in the solvent and tend to simulate asphaltenes and wil to some degree co-precipitate with them.
By way of comprise, the new method of asphaltic component analysis demonstrates that the so-called asphaltenes, as determined by insolubility in heptane, actually consist of about 50% microcrystalline waxes, on the average, and about 50% true asphaltic material. In other words there is less "true" asphaltic material in crude oils than heretofore thought. It is to be emphasized that this asphaltic material recovered in the improved separation procedure will be less adulterated; and, as a result, not subjected to the rapid deterioration of the asphaltenes which contain up to 50% waxes. In addition, it is to be pointed out that a better separation of the waxes provides a greater yield of material suitable as a valuable source of distillate. Asphaltic materials cannot be cracked to distillate. Where they are left in distillate cuts, they mostly form gas and coke, causing difficulties in the refining operations. Actually, as heretofore noted, the presence of the heat labile materials prevents the total desulfurization of the residual fuels in the present-day catalytic hydrodesulfurization units. The commercial desulfurization of residual fuels containing asphaltenes achieves a reduction of the sulfur content to no better than 0.2% to 0.3% while the same residual fuel can be desulfurized to less than 0.01% sulfur provided the asphaltic materials are removed. Furthemore, catalyst life can be extended from one year to about eight years.